Present regulatory conditions in the automotive market have led to an increasing demand to improve fuel economy and reduce emissions in present vehicles. These regulatory conditions must be balanced with the demands of a consumer for high performance and quick response in a vehicle. Variable displacement internal combustion engines (ICEs) provide for improved fuel economy and torque on demand by operating on the principal of cylinder deactivation.
During operating conditions that require high output torque, every cylinder of a variable displacement ICE is supplied with fuel and air (also spark, in the case of a gasoline ICE) to provide torque for the ICE. During operating conditions at low speed, low load and/or other inefficient conditions for a variable displacement ICE, cylinders may be deactivated to improve fuel economy for the variable displacement ICE and vehicle. For example, in the operation of a vehicle equipped with an eight cylinder ICE, fuel economy will be improved if the ICE is operated with only four cylinders during low torque operating conditions by reducing throttling losses. Throttling losses, also known as pumping losses, are the extra work that an ICE must perform to pump air around the restriction of a relatively closed throttle plate and pump air from the relatively low pressure of an intake manifold through the ICE and out to the atmosphere. The cylinders that are deactivated will not allow air flow through their intake and exhaust valves, reducing pumping losses by forcing the ICE to operate at a higher throttle plate angle and a higher intake manifold pressure. Since the deactivated cylinders do not allow air to flow, additional losses are avoided by operating the deactivated cylinders as “air springs” due to the compression and decompression of the air in each deactivated cylinder.
Previous variable displacement ICE's suffered from driveability issues created by their control systems. A transition in a previous variable displacement eight cylinder ICE to six or four cylinder operation created noticeable torque disturbances that affected the operation of the vehicle. These torque disturbances were generally considered undesirable by consumers. The inability to control throttle position as a function of displacement in previous variable displacement ICEs contributed to the problem of torque disturbances. The introduction of new engine control devices such as electronic throttle control (ETC), engine controllers, position sensors for pedal controls, and other electronics has enabled tighter control over more functions of an ICE.